1. Field of the Invention
This invention relates to a rotation transmitter using balls and, more particularly, to a rotation transmitter which comprises a worm shaft with a central hourglass-shaped portion having a circulation path constituted by a helical ball guide groove and a bore penetrating the hourglass portion, a plurality of metal balls accommodated in the circulation path and a worm wheel with the outer periphery thereof formed with ball fitting grooves in which the metal balls are fitted.
2. Prior Art Statement
Japanese Pat. Publication No. SHO 38-22759 discloses a speed reduction device in which an hourglass worm shaft has a helical depressed line such that a plurality of balls are accommodated in the depressed line to form a raised line, and the raised line formed of the balls is continuously or closely fitted in a depressed line of a worm wheel for transmission of rotation.
In the conventional speed reduction device, however, the worm shaft has an axially centrally extending bore which communicates with the opposite ends of the helical depressed line formed in the outer periphery. The axial bore is sealed at each end by a collar. Each collar is formed with a guide hole or path which extends such that it is first curved from the axis of the collar toward the outer periphery thereof and is then curved to extend in a tangential direction so as to communicate with each end of a helical ball guide path constituted by the depressed lines of the worm shaft and worm wheel.
The guide hole or path is curved sharply and particularly perpendicularly at its section communicating with the axial bore in the worm shaft. In such curved portions of the hole or path, the balls are difficult to roll or move and liable to seize due to the generation of frictional heat.
In such rotation transmitter having the raised line formed of a plurality of balls which are closely fitted in a depressed line of the worm shaft, in order to efficiently transmit the rotation of the worm shaft to the worm wheel, it is desired that the plurality of closely fitted balls roll smoothly for movement along the helical depressed line and axial bore formed in the worm shaft.
In the well-known speed reduction device, the worm shaft with the plurality of balls closely fitted in the helical ball guide path is surrounded by a notched hollow cylinder and supported by a casing such that its axis and the axis of the worm wheel cross each other when it is in mesh with the worm wheel. With this structure, however, the assembly is complicated and the state of mesh between the worm shaft and worm wheel cannot be readily adjusted.